The answer is , of course ,that the Iron Bank is more than just a bank. We don't know exactly how it functions and to what ends, but the hints that have been given, as early as in AGoT, about how it was foolish to mess with the Bank, how it will have it's due, give us reason to think of it as something more.Even that early statement seems mildly ominous. Since then, it's been observed that leaders who don't live up to their agreement with the Bank may pay with their lives.
In the meantime, we know that the FM act, in part, as intelligence agents..Why are all the bits of information Arya brings back to the House " good to know " ?..Before she begins her assassin specific training , she's being trained how to spy. If the HoB&W is strictly a religious institution , what purpose would that spying serve ?
We've seen an example of the kind of price exacted for FM services .. 2/3 of the person's wealth ,e.g... If, as has been hinted, the IB has been using FM on a regular basis to deal with royal defaulters ( often enough for it to become popular suspicion ) , how can it still be so rich ? Unless of course , it doesn't have to pay...unless it would just be the right hand passing money to the left..
And if the IB uses FM as enforcers , why wouldn't they make use of the FM's other area of expertise..intelligence..to get a very accurate picture of what's going on in each of the 7 kingdoms ?
No, the Iron Bank is obviously a political player, we just don't know their endgame yet.
ETA; It does make me think of the duality in the House of Black and White's name and as seen on it's door,white on one side black on the other with one face in the centre.
Edited by bemused, 04 January 2012 - 10:45 PM.